1. Field of the Invention
The present invention relates to a laser scanning unit. More particularly, the present invention is directed to a laser scanning unit for use in a laser printer and the like, in which a rotative noise reducing portion is formed at an edge portion where two mirror surfaces of a polygon mirror join, which deflects laser beams generated by a laser diode or a surface emitting laser diode into a pickup surface such as a photosensitive drum in a scanning direction, so that noise generated by rotation of the polygon mirror can be reduced.
2. Description of the Related Art
Recently, with the increasing popularity of laser printers, a variety of laser scanning units have been developed. The scanning unit is an optical system which scans laser beams upon a pickup surface to realize a desired picture on the pickup surface in a dotted form or to read out a manuscript through a picture. Generally, the laser scanning unit includes an emitting portion which emits laser beams, a deflecting portion which deflects laser beams in a scanning direction against the pickup surface, and a pickup portion which scans laser beams into the pickup surface in a dotted form.
A conventional laser scanning unit will be described with reference to the accompanying drawings.
As illustrated in FIGS. 2A and 2B, depending on the rotative direction of a polygon mirror which acts as a deflecting means, a high pressure area A (pressure surface portion illustrated by dots in FIG. 2a) is formed at a mirror surface in a rotative direction, around an edge 100 where two adjacent mirror surfaces a and b among polygonal mirror surfaces of the laser scanning unit join. A low pressure area B (minor pressure surface portion) is formed at the mirror surface opposite to the rotative direction. To achieve uniform pressure difference between the high pressure area and the low pressure area, as air flows into the low pressure area, a vortex flow having uneven fluid is formed at the low pressure area. As a result, the conventional laser scanning unit has a problem with respect to noise which occurs due to the vortex flow.